The selective movement of macromolecules between the nucleus and cytoplasm is fundamental to the maintenance of the distinct identities of these two compartments. It is becoming increasingly clear that nuclear activity during cell growth and development may be modulated at least in part at the level of import of regulatory molecules such as transcription factors and protein kinases. The gated channels which mediate this traffic of macromolecules are the nuclear pore complexes. These are extremely elaborate multiprotein assemblies, each of which functions in both nuclear protein import and RNA export. Recent ultrastructural analyses suggest a total mass for each pore complex in excess of 10(8)D, only 10% of which can be accounted for by the 10-15 pore complex proteins so far identified. The goals of this proposal are to purify and characterize at the molecular level members of a group of four-five proteins which form a subcomplex within the nuclear pore. This subcomplex was identified employing a monoclonal antibody against a 170kD protein previously produced in this laboratory. The subsequent isolation of cDNAs and additional immunological reagents will provide the tools with which to define functions and interactions of the individual members of this subcomplex, both in vivo and in vitro. This in turn should help shed some light on the as yet obscure mechanisms of nuclear activity at the level of nuclear transport.